DP Chemistry (last assessment 2024)

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Question 19M.2.sl.TZ1.3b

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Date May 2019 Marks available [Maximum mark: 2] Reference code 19M.2.sl.TZ1.3b
Level sl Paper 2 Time zone TZ1
Command term Calculate Question number b Adapted from N/A
b.
[Maximum mark: 2]
19M.2.sl.TZ1.3b

This question is about compounds of sodium.

(b)

Sodium peroxide, Na2O2, is formed by the reaction of sodium oxide with oxygen.

2Na2O (s) + O2 (g) → 2Na2O2 (s)

Calculate the percentage yield of sodium peroxide if 5.00 g of sodium oxide produces 5.50 g of sodium peroxide.

[2]

Markscheme

n(Na2O2) theoretical yield «=  5.00  g 61.98  mo l − 1 » = 0.0807/8.07 × 10−2 «mol»
OR
mass Na2O2 theoretical yield «=  5.00  g 61.98  mo l − 1 × 77.98 gmol−1» = 6.291 «g»  [✔]

% yield «=  5.50  g 6.291  g  × 100» OR « 0.0705 0.0807 x 100» = 87.4 «%»  [✔]

 

Note: Award [2] for correct final answer.

Examiners report

Many candidates were able to correctly calculate the % yield but some weaker candidates just used 5.0/5.5 to find %.

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